Tag Archives: HSQC

In my first two posts on using 1D and 2D NMR methods to assign the peaks of quinine (Figure 1), I looked at the 1H and 13C spectra.

Figure 1. Structure of quinine

In this post, I’m moving on to look at the 1H-13C HSQC spectrum. It’s worth spending a brief moment recapping what HSQC is all about and what info it gives you. In a nutshell, the HSQC experiment correlates proton and carbon chemical shifts over one chemical bond. Another way to put this is that a cross-peak in an HSQC spectrum says, “The proton with this chemical shift is directly attached to the carbon with that chemical shift”. By convention, HSQC spectra are presented with 1H shifts along the horizontal axis and 13C shifts along the vertical axis.

Some variants of HSQC also encode into the phases of the cross-peaks additional information about how many hydrogen atoms are attached to each carbon atom. This is sometimes referred to as multiplicity or DEPT editing. In the multiplicity-edited HSQC spectrum, it is conventional for the CH and CH3 groups to have positive phase, and the CH2 groups to have negative phase, just as in a DEPT-135 spectrum. Figure 2 shows the multiplicity-edited HSQC (“HSQC-ME”) spectrum of our 400 mM quinine sample. The CH2 signals are shown in blue and the CH and CH3 signals in red.

Figure 1. Structure of quinine

In my last blog post I introduced silicon NMR on Spinsolve and showed a variety of 1D 29Si{1H} and 29Si-1H DEPT spectra. In this post I’m moving on to talk about some 2D experiments that are useful for silicon studies. One of the most useful and widely used of those is the 1H-29Si HMBC experiment, which correlates proton and silicon chemical shifts over two or more chemical bonds. For example, Figure 1 below shows a 1H-29Si HMBC spectrum of the 1,1,3,3,5,5-hexamethyltrisiloxane sample I used before, collected in around 17 minutes. The 1H spectrum is shown along the horizontal axis of the 2D spectrum, and the 29Si spectrum is shown along the vertical axis.

One of the most widely-used 2D techniques these days is the HSQC (Heteronuclear Single Quantum Correlation) experiment. In the world of “small molecule” NMR, HSQC is most frequently used to correlate protons and carbons over one chemical bond.